MH3022, MH3024 and MH3026 Material Handlers Hydraulic System Caterpillar

Pilot Hydraulic Schematic

Illustration 1	g03861732
Pilot Hydraulic System (1) Shift piston (2) Modulation valve (3) First gear valve (4) Oscillating axle cylinders (5) Fore boom lowering control valve (if equipped) (6) Boom lowering control valve (left) (7) Boom lowering control valve (right) (8) Stick lowering control valve (9) Boom lowering control valve (left) - for smart boom (if equipped) (10) Boom lowering control valve (right) - for smart boom (if equipped) (11) Control valve (multi combined anti drift valve - if equipped) (12) Auxiliary valve directional solenoid (if equipped) (13) Auxiliary flow valve port "B" (if equipped) (14) Auxiliary flow valve port "A" (if equipped) (15) Bucket pilot pressure sensor - port "A" (16) Stick pilot pressure sensor - port "A" (17) Boom pilot pressure sensor - port "A" (18) Fore Boom pilot pressure sensor - port "A" (if equipped) (19) Pilot filter (20) Steering priority valve (21) Boom down pilot pressure switch (22) Fore Boom pilot pressure sensor - port "B" (if equipped) (23) Boom pilot pressure sensor - port "B" (24) Check valve (boom rod end) - port "B" (25) Check valve (boom head end) - port "A" (26) Stick pilot pressure sensor - port "B" (27) Bucket pilot pressure sensor - port "B" (28) Drift reduction valve (bucket valve - port "A") (29) Swing brake (30) Medium pressure pilot pump (31) Swing pump (32) Main pump (33) Hydraulic oil tank (34) Relief valve (medium pressure creation) (35) Relief valve (pilot pressure creation) (36) Gear shift solenoid valve (37) Travel direction solenoid valve (38) Travel activation solenoid (39) Main pump limit solenoid (40) Swing pump control pressure switch (41) Swing pump control solenoid (42) Travel motor swash plate angle limit solenoid (43) Pilot manifold (44) Oscillating axle solenoid (45) Swing brake solenoid (46) Heavy lift solenoid (if equipped) (47) Implement lockout solenoid (48) Blade pilot pressure sensor (49) Pilot system oil pressure sensor (50) Medium pressure pilot pump displacement control solenoid (51) Auto brake safety valve (52) Right joystick pilot control (53) Travel pedal (54) Fore boom pedal (if equipped) (55) Left joystick pilot control (56) Blade/Stabilizer control lever (57) Medium pressure control valve (58) Smart boom control solenoid (if equipped) (59) Pilot oil swivel (60) Main oil swivel

The pilot manifold is located behind the cab and below the step leading to the top of the machine.

The pilot manifold performs many functions. Solenoid valves that are installed in the pilot manifold direct pilot oil flow to components on the machine. The pilot manifold performs the following functions:

• Controls transmission clutch engagement for gear selection

• Supplies pilot oil to the joysticks and pedals in order to operate the main control valve spools

• Activates the heavy lift option

• Release the swing parking brake

• Generate power shift pressure for controlling the medium pressure/pilot pump

• Locks and unlocks the oscillating axle cylinders

• Controls travel motor displacement change valve

• Limits the swing system pressure relief valve

• Supplies oil to the medium pressure control valve

Piston Pump

Illustration 2	g03861741
Right side view (30) Medium pressure pilot pump

A pressure signal line is connected from the pump outlet to the pilot manifold Q+ solenoid and back to pump port "X". At higher oil flow demand (medium pressure valve activated or pilot pressure too low) the Q+ solenoid activates and the pump adjusts to a higher displacement.

Medium pressure pilot pump (30) supplies oil flow to the medium pressure and pilot hydraulic systems. Oil flow from the pump is used to operate various components.

The oil from pump (30) flows to pilot oil filter (19) and to displacement control solenoid valve (50).

A controlled amount of oil from displacement control solenoid valve (50) flows back to pump (30) in order to control pump output.

The filtered oil flows to steering priority valve (20) before flowing through the brake valve to pilot manifold (43).

Pilot manifold (43) is where medium pressure and pilot oil pressures are created. The pilot manifold is also the point of distribution for all of the pilot oil flow.